Many pressure transducer assemblies are configured to include a header portion that houses a sensing element and a port portion, wherein the header is attached to the port portion. The attachment between the header and port portions enable electrical connection between the sensing element and the remaining electronic components within the pressure transducer assembly. The header/port attachment serves to seal and contain the pressure media in the manifold/pipe, etc., while isolating the electrical components from the media, and allowing assembly of the electronics to the pressure sensing sub assembly.
Typically, the header portion is welded to the port portion and, in many embodiments, the header portion comprises a threaded section that mates with a corresponding threaded section on the port portion, as illustrated in FIG. 1. The threads are provided to take the load off the welded section. In use, the welded portion may experience stresses due to internal pressures in the design. These stresses include the hoop stress or tangential stress, and radial stress.
It was once believed that the thread would aid in removing the tensile stress from the weld area. However, several micrographs of experimental and production designs indicate that the threads may become disengaged during welding, thereby placing tensile stress on the welded area. The weld is typically an electron beam weld, and as the material melts to form the weld, any preload on the structure may be removed. Consequently, this increases the stress on the welded portion and reduces the fatigue life of the pressure transducer assembly considerably.